Intramolecular C–H insertion vs. Friedel–Crafts coupling induced by silyl cation-promoted C–F activation

Oliver Allemann,Jay S Siegel,Kim K Baldridge

doi:10.1039/c5qo00170f

Abstract

Silyl cation-promoted aryl C–F activation can lead to formal C–H activation and the formation of new C(ar)–C(alkyl) bonds.

Highlights

Silyl cations activate even highly stable C–F bonds.[1,2] Prominent cases include hydrodefluorinations of fluoroalkanes, by simple[3,4,5] as well as bridging[6,7] cationic silanes, and catalytic intramolecular coupling of a fluoroarene with a non-functionalized arene.[8,9] triisopropylsilylium hexachlorocarba-closo-dodecaborate (1), induces the cleavage of an aryl carbon–fluorine bond allowing a proximal aryl moiety to attack the incipient phenyl cation
Intramolecular C–H insertion vs. Friedel–Crafts coupling induced by silyl cation-promoted C–F activation† Cite this: Org
Reaction of 2-fluoro-2′-methylbiphenyl (2) with 5 mol% of [iPr3Si][CHB11H5Cl6] (1) and stoichiometric dimethyldimesitylsilane (DMDMS) illustrates the fundamental C–F/C–H activation couple (Scheme 2); wherein 1 serves as catalytic initiator and DMDMS serves as Brønsted base and pro-Lewis acid catalyst

Summary

Introduction

Silyl cations activate even highly stable C–F bonds.[1,2] Prominent cases include hydrodefluorinations of fluoroalkanes, by simple[3,4,5] as well as bridging[6,7] cationic silanes, and catalytic intramolecular coupling of a fluoroarene with a non-functionalized arene.[8,9] triisopropylsilylium hexachlorocarba-closo-dodecaborate (1), induces the cleavage of an aryl carbon–fluorine bond allowing a proximal aryl moiety to attack the incipient phenyl cation. Intramolecular C–H insertion vs Friedel–Crafts coupling induced by silyl cation-promoted C–F activation† Cite this: Org. Chem. Deuterium-labeling experiments suggest an insertion of a phenyl cation into the C–H bond.

Results

Conclusion